To regulate the body temperature of a patient so as to prevent hypothermia in the patient, a convective blanket that provides a constant stream of warmed air to the patient is used. Convective blankets are inflated by air convective warmers. Most, if not all, air convective warmers produce a high level of noise, at least for some of the patients and others who may be close to the machine. This is because blowers are utilized in the convective warmers to propel a stream of air, heated or otherwise, from an air inlet to an air outlet, in order to inflate the convective blanket. The noise from the blower, along with the air stream flow through the convective warmer, tend to produce substantial noise. Such substantial noise could be an annoyance to the patient. The noise from the air convective warmer therefore needs to be reduced.
Prior to the instant invention, attempts have been made to reduce the noise of air convective warmers. Such attempts include U.S. Pat. No. 6,126,393 and its related U.S. Pat. No. 6,254,337. These patents disclose the configuration of an air blower unit in which the air inlet is pointed toward the surface onto which the housing of the air blower unit rests. The outlet for the air blower is provided at a side of the housing, and is coupled to an air hose that has an elbow bent between 45° and 90°. Thus configured, noise generated by the warmer allegedly is absorbed by the elbow, and the noise waves that are not absorbed by the elbow are allegedly reflected downwardly onto the support surface by the elbow.
Another attempt to reduce the noise of an air blower is disclosed in U.S. Pat. No. 5,733,320. In the '320 device, noise cancellation components are used. Such noise canceling components include an input sensor such as a microphone, a sound source such as a loud speaker, a noise cancellation controller and an optional error microphone. An audio noise cancelling signal, 180° out of phase with the noise measured by the input microphone, is output from the loudspeaker to cancel out the noise.
Yet another attempt to reduce the noise level of an air convective warmer is disclosed in U.S. Pat. No. 7,037,068, assigned to the assignee of the instant application. In the '068 device, indentations are provided at the interior surface of the plenum chamber of the warmer to suppress the noise. The disclosure of the '068 patent is incorporated by reference herein.